Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Scydmaenidae

= Anisosphaeridae.

Ant-like Stone-beetles.

General appearance. 0.7–2.2 mm long. Body length/maximum body width 1.6–2.55. Elytral length/pronotal length 1.6–2.6. Base of prothorax not or scarcely narrower than the combined elytral bases, or distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width, or distinctly narrower than greatest elytral width. Beetles elongate-oval to elongate; conspicuously necked; conspicuously waisted. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Eyes strongly protuberant, or not strongly protuberant; bristly, or without bristles. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a reduced mola, or without a mola; with well developed prosthecae to without prosthecae. The mandibular apices simple. The incisor edges of the mandibles simple, or with a single tooth, or with two or more teeth (being variable in Scydmaeninae). The maxillae with distinct galea and lacinia apically to the palp. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae short to about half the insect's head to tail length; 11 segmented; filiform (or moniliform), or clubbed. Antennal insertions visible from above, or hidden from above.

Cervical sclerites present, or absent. Prothorax about as long as wide to longer than wide. Pronotal length/maximum pronotal width 0.6–1.55. The pronotum with lateral keels (pronotal carinae), or without lateral keels (some Scydmaeninae); keels when present, complete, or incomplete (when present in Scydmaeninae). Prothorax without notopleural sutures. Hind corners of the thorax not extended rearwards into sharp points. Scutellum conspicuous, or highly reduced to absent (some Scydmaeninae); when applicable, elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. The prosternal process present (Cephenniini), or absent (in some Scydmaeninae); when present, complete (Cephenniini), or incomplete; when applicable, falling short of the mesoventrite, or moderately or strongly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities open behind externally; broadly open; medianly confluent, or narrowly separated; slightly transverse, or circular to longer than wide; without lateral extensions; internally open, or internally closed by a slender bar, or broadly closed internally. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity. The mid-leg coxal cavities narrowly separated, or moderately to widely separated; not or scarcely oblique; open laterally, or closed laterally. Hind-leg coxae widely separated; extending laterally to meet the elytra (Cephenniinae), or not markedly extended laterally (Scydmeninae). Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytral length/maximum width across the elytra 1.05–1.7. Elytra covering most to all of the abdomen; exposing no more than part of the terminal tergite; not truncate; glossy; non-glabrous (clothed in fine, sparse hairs), or glabrous. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed, or absent or much reduced. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 6; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles. The male external genitalia staphylinoid.

Adult habitat, ecology. Land-dwellers (but found near water); predacious (on small arthropods, especially mites); in decaying plant material, or in rotting wood, or under bark, or on shed fur or feathers, or under stones (or in moss, generally in damp places).

Larvae. Mature larvae minute (less than 3 mm long). The larvae elongate and more or less parallel-sided, or oblong to ovate; C-shaped in lateral view, or not C-shaped. Body somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized, or dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 2 segmented, or 3 segmented. Stemmata present, or absent; on either side of the larval head when present, 1, or 3. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 2 segmented (Eutheia only), or 3 segmented. The labium without ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 9, or 10. Tergum 9 of the abdomen entirely dorsal. The abdomen having functional spiracles on anterior segments (these annular); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae predacious (taking mites and other small prey); in decaying plant material, or in rotting wood, or under bark, or in shed fur or feathers, or under stones (or in moss, generally in damp places).

Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Staphilinoidea.

Representation in Britain and Ireland, and worldwide. About 4500 species worldwide; genera about 80. 30 species in Britain; genera in Britain 8; Euconnus, Eutheia, Cephennium, Microscydmus, Neuraphes, Scydmaenus, Scydmoraphes, Stenichnus. E.g., Scydmaenus tarsatus.

General comments. Narrow-necked beetles with a characteristically waisted body form, sometimes with oval elytra; the eyes coarsely granular; the fore coxae with the trochanters hidden.

Illustrations. • Cephennium, Euconnus (2 spp.), Euthia (2 spp.), Neuraphes, Scydmaenus, Scydmoraphes, Stenichnus (3 spp.), with Pselaphidae: Fowler 3, 76 (1889). • Fowler 3, 76 (1889): original legend.. • Euconnus maeklini, Neuraphes (2 spp.), Scydmaenus rufus, Stenichnus (2 spp.): Fowler 6, 11 (1913). • Fowler Suppl. 11, 1913: original legend.. • Scydmaenus tarsatus (Rye & Fowler VI2). • Cephennium gallicum (from Joy).


To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: the families of Coleoptera. Version: 16th May 2016. delta-intkey.com’.

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